Test email sending with no controller

My application sends many emails. The official doc tells how to test emails sending with the HTTP client profiler.

But I obviously don't have a Controller for each email I'm sending.

How can I test my emails that are not triggered from a controller ? (I mean not from a request context).

---

Further detail on my specific case

I'm using a listener to trigger calls to a service which is doing the "email routing"
What I'd like to do here, is fire some events and check what is sent (the email body, title, recipients, ...)